Castanospermum Australe Cunn et. Fras (Fabiaceae) is medicinal and toxic plant which is indigenous to Australia, but cultivated in Pakistan.
The present investigation deals with a study of the saponin and terpenic constituents of Castanospermum australe and the evaluation of their bioactivity
The thesis is divided into two parts. Part-1 describes a study conducted on the saponin and terpenic constituents of Castanopermum australe. Part-II records an investigation of the pharmacological screening of the saponins
Part-1 contains the structural studies on eight new saponins, designated as castaraleside A-H which have been isolated from the butanol soluble parts of the methanolic extract of the leaves of the Castanospermum australe. The structures of these saponins were elucidated on the basis of spectroscopic techniques and chemical methods. These involved IR, 1H-NMR (Spin decoupling, 2D-J-resolved, COSY-45, NOESY experiments), 13C-NMR (DEPT, hetero-COSY experiments), EI-MS (negative and positive ion mode), HR-MS as well as acidic hydrolysis and alditol acetate analysis by GC-MS
During the course of isolation, the identity of an artefact of bayogenin was also established. The ethyl acetate fraction of the methanolic extract of this plant also furnished four terpenic constituents and these were identified as stigmasterol, lupeol, a-amyrin and B-amyrin
Part-II includes the brine shrimp bioassay, crown gall tumour bioassay, insecticidal activity, toxicity on rats and mice, analgesic activity and cholinergic activity. The brine shrimp bioassay of the saponis of Castanospermum australe gave LD50 value as 81.16 μg/ml which is comparable to moderately potent compounds. Crown gall tumour activity of saponin showed that 100% tumours were inhibited with 25 μg/ml. The insecticidal activity of saponin against Callosobruchus analis revealed LD50 as 38 μg/cm2 which is orally toxic. Toxicity determination on rats and mice showed LD50 for oral as 400 mg/kg and i.p. as 35 mg/kg and this suggests that these are toxic in lower doses as compared with those of the saponins obtained form other plants.
The analgesic activity of the saponin administrated i.p. at dose of 12.5, 25 and 50 mg/kg showed analgiesic activity of the order 25, 45, and 75% respectively. Thus, it may be concluded that the analgesic activity of the saponin of Castanospermum australe can be achieved with higher doses as compared to the saponins of Dolichos falcatus and at lower doses compared to the saponin of panax notoginseng. The cholinergic activity of saponis of Castanospermum australe showed that the dose range of 1-30 mg/kg produces fall in blood pressure and heart rate in anesthetized rats. Pretreatment of atropine abolished both hypotensive and bradycardiac effects. In isolated guineas pig- atria the a saponin the saponin produce negative inotropic and chronotropic responses at 10-100 μg/ml, when tested on isolated guinea-pig ileum, its produces contractile responses similar to that of acetylcholine. All these responses of saponin and acetylcholine on cardiac and smooth muscle preparations were completely blocked by atropine (0.1 mg/kg). Thus saponin appear to mediated all its effects through mechanism similar to that acetycholine.